Methylchlorosilanes are well known for their many uses, including as raw materials in the production of polysiloxanes and other materials that may be used in applications such as the coating of titanium dioxide, which may, for example, be incorporated into materials such a plastics. One particularly useful methylchlorosilane is dimethyldichlorosilane, which is used in many industrial processes, including the preparation of oils and gums. These materials are, for example, useful starting materials in the manufacture of silicones.
Processes for producing methylchlorosilanes are well known to persons skilled in the art. For example, as described in the background of U.S. Pat. No. 4,645,851, according to the “direct synthesis” or “Rochow synthesis” processes, methylchlorosilanes may be produced directly by reacting methyl chloride with solid silicon in the presence of a copper catalyst.
The reaction for producing dimethyldichlorosilanes is summarized in Formula I below:2CH3Cl+Si→(CH3)2SiCl2   Formula IHowever, in most industrial processes, the reaction of methyl chloride with silicon will also produce (CH3)SiCl3, (CH3)3SiCl, CH3HSiCl2, (CH3)2HSiCl, and other molecular species.
As noted above, in the formation of methylchlorosilanes, one may use copper as a catalyst. One may also use other substances such as zinc, zinc halides, aluminium, tin, manganese, nickel, silver, cobalt, and potassium chloride to promote the formation of methylchlorosilanes.
Zinc has proven to be a particularly useful promoter of the formation of methylchlorosilanes when it is used in combination with copper. However, although zinc is an effective promoter, its use suffers from a number of drawbacks.
First, it is often difficult to provide a consistent level of zinc. This reduces the operability of the system. Second, known processes often suffer from exotherm induced temperature spikes. Third, in these processes there is often instability of the reaction temperature. Fourth, most processes that use zinc inject it in the presence of an inert gas, such as nitrogen, which dilutes the methyl chloride reactant. Fifth, a separate means for adding the zinc is necessary, which adds to the cost of the process. Sixth, known catalysts using zinc have undesirable fluidization properties. Seventh, these catalysts have undesirably low levels of selectivity to the dimethyldichlorosilane. Eighth, as the reaction proceeds, it is difficult to retain the desired level of selectivity. Ninth, the addition of zinc in certain forms may pose safety problems, because metallic zinc and certain other zinc compounds can react with methyl chloride and copper oxide to cause very exothermic reactions.
Thus, there remains a need to develop better ways to optimize the formation of dimethyldichlorosilane. The present invention provides one solution by allowing for the improvement in the selectivity of the formation of dimethyldichlorosilane and through the making of a catalyst in which copper oxide and zinc oxide are in intimate contact in an agglomerated particle.